After an element has completed its animation, the callback still shows that the element is animated. I posted a demo here: https://jsfiddle.net/5V5M3/

$(".block").animate({
    "left": "+=50px"
}, "slow", function() {
    alert($(".block").is(':animated'));
});

I can hack around it by basically using a setTimeout:

$(".block").animate({
    "left": "+=50px"
}, "slow", function() {
    setTimeout(function() { alert($(".block").is(':animated')) }, 0);
});